Oil fields in its initial operation stage are produce by using its natural energy, which is known as primary recovery. As the reservoir loses energy it requires the injection of gas or water in order to restore or maintain the reservoir pressure, this stage is called secondary recovery. When the secondary recovery methods become ineffective it is necessary to apply other more sophisticated methods such as steam injection, chemicals, microorganisms, etc. These methods are known as tertiary or enhanced oil recovery (EOR). Some important oil fields in Mexico are entering the third stage.